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    1. Verbal Fluency TestGradeA
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    16,361Registered studies name a cognitive test in an outcome measure11,688 name a test you can run hereExplore the studies
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  5. /Symbol Coding

Clinical trials data

Symbol Coding in clinical trials: 1,457 registered studies

Every registered study on ClinicalTrials.gov that names Symbol Coding in an outcome measure: the conditions it is used in, how often it is a primary outcome, the tests it is named with, and how large the studies are.

Registered studies name it in an outcome measure
1,457
Name it in a primary outcome, 31%
451 of 1,457
Against similar tests
Of studies started 2021 to 2025 name it, against 8.9% in 2016 to 2020
8.9%
By year
Median participants per study
70
By phase
Try the Symbol Key GameTry Symbol Coding

The conditions it is used in

Each study counted once in each condition group it falls in.

  1. Multiple sclerosis375 studies, 93 as a primary outcome

  2. Depression and bipolar disorder143 studies, 37 as a primary outcome

  3. Dementia and Alzheimer's117 studies, 41 as a primary outcome

  4. Aging, frailty and exercise116 studies, 34 as a primary outcome

  5. Sleep and sleep disorders89 studies, 29 as a primary outcome

  6. Mild cognitive impairment84 studies, 38 as a primary outcome

  7. Pain and fatigue82 studies, 17 as a primary outcome

  8. Stroke61 studies, 13 as a primary outcome

  9. Substance use and addiction60 studies, 17 as a primary outcome

  10. Obesity and diabetes59 studies, 27 as a primary outcome

  11. Cancer58 studies, 27 as a primary outcome

  12. Healthy volunteers56 studies, 18 as a primary outcome

  13. Cardiovascular disease46 studies, 10 as a primary outcome

  14. Brain injury and concussion43 studies, 17 as a primary outcome

  15. Schizophrenia and psychosis43 studies, 9 as a primary outcome

  16. Parkinson's disease41 studies, 10 as a primary outcome

  17. Cognitive impairment and decline40 studies, 18 as a primary outcome

  18. Anxiety, PTSD and OCD31 studies, 10 as a primary outcome

  19. Delirium, surgery and intensive care29 studies, 11 as a primary outcome

  20. Huntington's disease26 studies, 5 as a primary outcome

  21. COVID-19 and long COVID21 studies, 5 as a primary outcome

  22. ADHD9 studies, 2 as a primary outcome

  23. Hearing loss7 studies, 4 as a primary outcome

  24. Epilepsy7 studies, 0 as a primary outcome

  25. Lung disease4 studies, 1 as a primary outcome

  26. Autism1 study, 1 as a primary outcome

  27. Other conditions132 studies, 51 as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

How often it is a primary outcome

Symbol Coding is a primary outcome in 31% of its studies. Across the 11 processing speed tests with a page here, the median is 42%.

  1. Motor Sequence Task53% of 30 studies

  2. Serial Reaction Time48% of 27 studies

  3. Arithmetic Fluency Task47% of 101 studies

  4. Mirror Tracing Task43% of 23 studies

  5. Symbol Scan Task42% of 129 studies

  6. Paced Visual Serial Addition Test42% of 337 studies

  7. Simple Reaction Time40% of 210 studies

  8. Finger Tapping Task38% of 144 studies

  9. Pattern and Letter Comparison35% of 147 studies

  10. Symbol Coding31% of 1,457 studies

  11. Trail Making Test31% of 2,293 studies

Studies by start year

8.9% of the registered studies that started in 2021 to 2025 name it, against 8.9% of those that started in 2016 to 2020. 2026 is partly planned starts.
01002000: 1 studies, 0 with a test as a primary outcome20002001: 2 studies, 0 with a test as a primary outcome2002: 3 studies, 1 with a test as a primary outcome2003: 3 studies, 0 with a test as a primary outcome2004: 11 studies, 2 with a test as a primary outcome2005: 7 studies, 4 with a test as a primary outcome20052006: 8 studies, 5 with a test as a primary outcome2007: 14 studies, 3 with a test as a primary outcome2008: 14 studies, 6 with a test as a primary outcome2009: 18 studies, 4 with a test as a primary outcome2010: 28 studies, 11 with a test as a primary outcome20102011: 30 studies, 9 with a test as a primary outcome2012: 27 studies, 13 with a test as a primary outcome2013: 35 studies, 10 with a test as a primary outcome2014: 47 studies, 17 with a test as a primary outcome2015: 39 studies, 14 with a test as a primary outcome20152016: 72 studies, 19 with a test as a primary outcome2017: 71 studies, 20 with a test as a primary outcome2018: 83 studies, 30 with a test as a primary outcome2019: 94 studies, 30 with a test as a primary outcome2020: 79 studies, 20 with a test as a primary outcome20202021: 116 studies, 41 with a test as a primary outcome2022: 107 studies, 33 with a test as a primary outcome2023: 140 studies, 34 with a test as a primary outcome2024: 134 studies, 45 with a test as a primary outcome2025: 134 studies, 43 with a test as a primary outcome20252026: 131 studies, 35 with a test as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

Show as a table
Registered studies by start year
Start yearStudiesA test as a primary outcome
200010
200120
200231
200330
2004112
200574
200685
2007143
2008146
2009184
20102811
2011309
20122713
20133510
20144717
20153914
20167219
20177120
20188330
20199430
20207920
202111641
202210733
202314034
202413445
202513443
202613135

Phases and study sizes

By phase

  • Early phase 119 studies, 4 as a primary outcome
  • Phase 170 studies, 16 as a primary outcome
  • Phase 1/226 studies, 6 as a primary outcome
  • Phase 2191 studies, 43 as a primary outcome
  • Phase 2/320 studies, 7 as a primary outcome
  • Phase 3123 studies, 16 as a primary outcome
  • Phase 484 studies, 28 as a primary outcome
  • Not applicable710 studies, 243 as a primary outcome
  • Observational214 studies, 88 as a primary outcome

Participants per study

1020501002005001,000
  • Early phase 125 median, 18 to 36
  • Phase 127 median, 18 to 46
  • Phase 1/235 median, 16 to 68
  • Phase 264 median, 40 to 111
  • Phase 2/3187 median, 72 to 292
  • Phase 3323 median, 107 to 946
  • Phase 4100 median, 36 to 240
  • Not applicable60 median, 31 to 120
  • Observational100 median, 50 to 200
Participants per study. The bar spans the middle half of the studies in each phase, the mark is the median, and the axis is logarithmic. Phases with fewer than 10 studies that give a size are left out.
Show as a table
Participants per study that names Symbol Coding, by phase
PhaseStudies with a sizeMedianMiddle half
Early phase 1162518 to 36
Phase 1682718 to 46
Phase 1/2253516 to 68
Phase 21836440 to 111
Phase 2/32018772 to 292
Phase 3120323107 to 946
Phase 48310036 to 240
Not applicable7036031 to 120
Observational21110050 to 200

When trials measure it

Half of the primary outcomes that name Symbol Coding are measured within 12 weeks of the start, and the middle half from 3 weeks to 9 months. 420 primary outcomes give a duration.

Latest time point of each outcome

  • Within a day193 outcomes, 66 as a primary outcome
  • Up to 4 weeks205 outcomes, 59 as a primary outcome
  • 1 to 3 months383 outcomes, 112 as a primary outcome
  • 3 to 6 months221 outcomes, 73 as a primary outcome
  • 6 to 12 months165 outcomes, 49 as a primary outcome
  • 1 to 2 years110 outcomes, 28 as a primary outcome
  • Over 2 years104 outcomes, 33 as a primary outcome
  • No duration given76 outcomes, 31 as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

1,381 of the 1,457 outcome measures give a duration. A single visit counts as within a day.

Status, results, interventions and countries

Status

  • Recruiting278 studies, 88 as a primary outcome
  • Not yet recruiting82 studies, 21 as a primary outcome
  • Active, not recruiting91 studies, 30 as a primary outcome
  • Completed695 studies, 225 as a primary outcome
  • Stopped early113 studies, 28 as a primary outcome
  • Status unknown198 studies, 59 as a primary outcome

What they test

  • Behavioral302 studies, 112 as a primary outcome
  • Drug515 studies, 112 as a primary outcome
  • Device211 studies, 54 as a primary outcome
  • Dietary supplement79 studies, 32 as a primary outcome
  • Procedure36 studies, 7 as a primary outcome
  • Diagnostic test38 studies, 14 as a primary outcome
  • Biological35 studies, 3 as a primary outcome
  • Radiation9 studies, 2 as a primary outcome
  • Combination product10 studies, 5 as a primary outcome
  • Genetic2 studies, 0 as a primary outcome
  • Other332 studies, 120 as a primary outcome
  • None given94 studies, 43 as a primary outcome

Intervention types as registered. A study can list several; observational studies often list none.

Where their sites are

  • United States557 studies, 187 as a primary outcome
  • Canada147 studies, 33 as a primary outcome
  • Italy127 studies, 37 as a primary outcome
  • Spain122 studies, 36 as a primary outcome
  • United Kingdom108 studies, 17 as a primary outcome
  • Germany105 studies, 20 as a primary outcome
  • France104 studies, 19 as a primary outcome
  • China94 studies, 24 as a primary outcome
  • Denmark77 studies, 14 as a primary outcome
  • Belgium68 studies, 15 as a primary outcome
  • Netherlands66 studies, 11 as a primary outcome
  • Türkiye62 studies, 19 as a primary outcome

90 countries in all. A study with sites in several counts in each; 77 list no site.

Reported results

Completed studies with results posted on ClinicalTrials.gov, a results paper the registry links to the study, or both.

Completed studies that name Symbol Coding: 343 of 695, 49%

Every completed study with a cognitive outcome: 3,626 of 7,953, 46%

Completed studies that name Symbol Coding and every completed study, by how they reported results
ResultsCompleted studies that name Symbol CodingEvery completed study
Results on ClinicalTrials.gov and a paper100, 14%776, 10%
Results on ClinicalTrials.gov only90, 13%1,139, 14%
A results paper only153, 22%1,711, 22%
Neither352, 51%4,327, 54%

Tests named in the same studies

The library tests that studies naming Symbol Coding name most often beside it.
  1. 1

    Trail Making Test432 studies, 142 as a primary outcome

  2. 2

    Verbal Learning416 studies, 158 as a primary outcome

  3. 3

    Digit Span Test307 studies, 117 as a primary outcome

  4. 4

    Verbal Fluency293 studies, 112 as a primary outcome

  5. 5

    Stroop Color-Word Test271 studies, 107 as a primary outcome

  6. 6

    Category Fluency142 studies, 69 as a primary outcome

  7. 7

    Paced Visual Serial Addition Test103 studies, 48 as a primary outcome

  8. 8

    Short Story Recall78 studies, 38 as a primary outcome

  9. 9

    N-Back Task77 studies, 34 as a primary outcome

  10. 10

    Selective Reminding Task68 studies, 27 as a primary outcome

A test as a primary outcomeOnly in secondary or other outcomes

Compared over time

Studies per start year for Symbol Coding and the tests named with it most. Add or remove tests to compare.
Symbol Coding1,448 studies, 2000 to 2026
01252502000201020202026
Trail Making Test2,281 studies, 2000 to 2026
01252502000201020202026
Verbal Learning1,819 studies, 2000 to 2026
01252502000201020202026
Digit Span Test1,619 studies, 2000 to 2026
01252502000201020202026

The panel's testThe other tests chosenEvery panel has the same scale. 2026 is partly planned starts.

Show as a table
Registered studies per start year that name each test
Start yearSymbol CodingTrail Making TestVerbal LearningDigit Span Test
20001213
20012052
20023381
200338144
20041110144
2005714177
2006814134
200714212214
200814172819
200918292822
201028324237
201130473326
201227444236
201335605344
201447668249
201539859179
2016721039869
20177112210782
2018831179285
201994155122110
2020791227690
2021116172137122
2022107188138121
2023140228157164
2024134211144141
2025134210132147
2026131201123137

Explore the 1,457 studies

Filter by condition, phase, sponsor, status, country, intervention, outcome list, size and start year. Each study links to its record on ClinicalTrials.gov.
TestSymbol Coding

1,457 studies match. 451 name Symbol Coding in a primary outcome. Median size 70 participants. Median time to the primary outcome: 12 weeks.

Loading 1,457 studies; the filters turn on when they arrive.

By start year
0501001502000: 1 studies, 0 naming Symbol Coding in a primary outcome20002001: 2 studies, 0 naming Symbol Coding in a primary outcome2002: 3 studies, 1 naming Symbol Coding in a primary outcome2003: 3 studies, 0 naming Symbol Coding in a primary outcome2004: 11 studies, 2 naming Symbol Coding in a primary outcome2005: 7 studies, 4 naming Symbol Coding in a primary outcome20052006: 8 studies, 5 naming Symbol Coding in a primary outcome2007: 14 studies, 3 naming Symbol Coding in a primary outcome2008: 14 studies, 6 naming Symbol Coding in a primary outcome2009: 18 studies, 4 naming Symbol Coding in a primary outcome2010: 28 studies, 11 naming Symbol Coding in a primary outcome20102011: 30 studies, 9 naming Symbol Coding in a primary outcome2012: 27 studies, 13 naming Symbol Coding in a primary outcome2013: 35 studies, 10 naming Symbol Coding in a primary outcome2014: 47 studies, 17 naming Symbol Coding in a primary outcome2015: 39 studies, 14 naming Symbol Coding in a primary outcome20152016: 72 studies, 19 naming Symbol Coding in a primary outcome2017: 71 studies, 20 naming Symbol Coding in a primary outcome2018: 83 studies, 30 naming Symbol Coding in a primary outcome2019: 94 studies, 30 naming Symbol Coding in a primary outcome2020: 79 studies, 20 naming Symbol Coding in a primary outcome20202021: 116 studies, 41 naming Symbol Coding in a primary outcome2022: 107 studies, 33 naming Symbol Coding in a primary outcome2023: 140 studies, 34 naming Symbol Coding in a primary outcome2024: 134 studies, 45 naming Symbol Coding in a primary outcome2025: 134 studies, 43 naming Symbol Coding in a primary outcome20252026: 131 studies, 35 naming Symbol Coding in a primary outcome

2026 is partly planned starts. Not shown: 2 that started before 2000 and 7 planned to start after 2026.

Show as a table
Matching studies by start year
Start yearStudiesAs a primary outcome
200010
200120
200231
200330
2004112
200574
200685
2007143
2008146
2009184
20102811
2011309
20122713
20133510
20144717
20153914
20167219
20177120
20188330
20199430
20207920
202111641
202210733
202314034
202413445
202513443
202613135

Library tests named most

  • Symbol Coding1,457 studies, 451 as a primary outcome
  • Trail Making Test432 studies, 142 as a primary outcome
  • Verbal Learning416 studies, 158 as a primary outcome
  • Digit Span Test307 studies, 117 as a primary outcome
  • Verbal Fluency293 studies, 112 as a primary outcome
  • Stroop Color-Word Test271 studies, 107 as a primary outcome
  • Category Fluency142 studies, 69 as a primary outcome
  • Paced Visual Serial Addition Test103 studies, 48 as a primary outcome
  • Short Story Recall78 studies, 38 as a primary outcome
  • N-Back Task77 studies, 34 as a primary outcome

Largest condition groups

Phases

Participants

Lead sponsor: industry 273, NIH 5, other 1,179. Interventional 1,243, observational 214.

As a primary outcomeSecondary or other outcomeSymbol Coding

The studies, newest registration first

Each number opens the study's record on ClinicalTrials.gov.

Registered studies that match the filters, newest registration first, with the library tests each one names and the outcome list that names them.
StudyStartPhaseConditionsParticipantsLead sponsorStatusLibrary tests named, with the latest time point
NCT07902206Start2026PhaseNot applicableConditionsAging, frailty and exercise, Huntington's diseaseParticipants88Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Trail Making TestSecondary6 months
  • Stroop Color-Word TestSecondary6 months
  • Verbal FluencySecondary6 months
  • Symbol CodingSecondary6 months
NCT07898722Start2025PhaseNot applicableConditionsAnxiety, PTSD and OCD, Pain and fatigueParticipants40Lead sponsorOtherStatusCompletedLibrary tests named
  • Symbol CodingSecondary
NCT07898371Start2026PhaseObservationalConditionsMultiple sclerosisParticipants3,000Lead sponsorIndustryStatusRecruitingLibrary tests named
  • Symbol CodingSecondary3 years
NCT07897474Start2026PhaseObservationalConditionsSleep and sleep disordersParticipants100Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Trail Making TestPrimary
  • Stroop Color-Word TestPrimary
  • Digit Span TestPrimary
  • Symbol CodingPrimary
  • Psychomotor Vigilance TaskPrimary
NCT07893925Start2026PhaseNot applicableConditionsMultiple sclerosisParticipants38Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal LearningSecondary8 weeks
  • Symbol CodingSecondary8 weeks
NCT07890753Start2026PhaseObservationalConditionsAging, frailty and exerciseParticipants60Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Symbol CodingSecondary2 years
NCT07889271Start2024PhaseObservationalConditionsMultiple sclerosisParticipants300Lead sponsorOtherStatusCompletedLibrary tests named
  • Symbol CodingPrimary
NCT07884643Start2026PhaseNot applicableConditionsOther conditionsParticipants70Lead sponsorIndustryStatusRecruitingLibrary tests named
  • Stroop Color-Word TestOther outcome12 weeks
  • Symbol CodingOther outcome12 weeks
  • N-Back TaskOther outcome12 weeks
NCT07880418Start2026PhaseNot applicableConditionsMultiple sclerosisParticipants20Lead sponsorOtherStatusCompletedLibrary tests named
  • Verbal LearningSecondary5 weeks
  • Symbol CodingSecondary5 weeks
NCT07879924Start2026PhaseNot applicableConditionsDepression and bipolar disorderParticipants60Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Symbol CodingSecondary1 week
  • Choice Reaction TimeSecondary1 week
NCT07872982Start2026PhaseNot applicableConditionsDelirium, surgery and intensive careParticipants304Lead sponsorIndustryStatusNot yet recruitingLibrary tests named
  • Verbal LearningPrimary1 week
  • Symbol CodingPrimary1 week
  • Ordered Number Search TaskPrimary1 week
NCT07870291Start2026PhaseNot applicableConditionsObesity and diabetesParticipants105Lead sponsorOtherStatusActive, not recruitingLibrary tests named
  • Trail Making TestPrimary12 weeks
  • Symbol CodingPrimary12 weeks
NCT07870187Start2027PhasePhase 1ConditionsSubstance use and addictionParticipants70Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Symbol CodingPrimarysame day
  • Paced Visual Serial Addition TestPrimarysame day
NCT07868887Start2026PhaseObservationalConditionsMultiple sclerosisParticipants200Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Symbol CodingOther outcome12 months
NCT07857720Start2026PhaseNot applicableConditionsOther conditionsParticipants8Lead sponsorOtherStatusCompletedLibrary tests named
  • Stroop Color-Word TestPrimary1 week
  • Symbol CodingPrimary1 week
NCT07856043Start2026PhasePhase 1ConditionsDementia and Alzheimer's, Mild cognitive impairment, Cardiovascular diseaseParticipants18Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Trail Making TestSecondary12 weeks
  • Symbol CodingSecondary12 weeks
  • Selective Reminding TaskSecondary12 weeks
NCT07852572Start2027PhaseNot applicableConditionsAging, frailty and exerciseParticipants204Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Symbol CodingSecondary6 months
NCT07852156Start2026PhaseNot applicableConditionsMultiple sclerosis, Pain and fatigueParticipants42Lead sponsorOtherStatusRecruitingLibrary tests named
  • Symbol CodingSecondary2 weeks
NCT07848477Start2026PhaseNot applicableConditionsDepression and bipolar disorderParticipants60Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal LearningPrimary2 weeks
  • Digit Span TestSecondary2 weeks
  • Symbol CodingSecondary2 weeks
  • N-Back TaskSecondary2 weeks
  • Go/No-Go TaskSecondary2 weeks
  • Paired Associate LearningSecondary2 weeks
  • Probabilistic Reversal LearningSecondary2 weeks
  • Mnemonic Similarity TaskSecondary2 weeks
  • Affective Go/No-GoSecondary2 weeks
  • Grid Pattern Span TaskSecondary2 weeks
NCT07842302Start2026PhaseNot applicableConditionsMultiple sclerosis, Pain and fatigueParticipants80Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Trail Making TestSecondary6 months
  • Stroop Color-Word TestSecondary6 months
  • Verbal FluencySecondary6 months
  • Symbol CodingPrimary6 months
  • Paced Visual Serial Addition TestSecondary6 months
  • Selective Reminding TaskSecondary6 months
NCT07842146Start2026PhaseNot applicableConditionsDementia and Alzheimer's, Mild cognitive impairmentParticipants60Lead sponsorOtherStatusRecruitingLibrary tests named
  • Verbal FluencySecondary11 months
  • Symbol CodingSecondary11 months
  • Category FluencySecondary11 months
  • Delayed Recall ModuleSecondary11 months
NCT07836478Start2026PhaseObservationalConditionsCancerParticipants60Lead sponsorOtherStatusNot yet recruitingLibrary tests named
  • Verbal LearningSecondary5 years
  • Symbol CodingSecondary5 years
  • Complex Figure Copy and RecallSecondary5 years
  • Corsi Block-Tapping TestSecondary5 years
NCT07833748Start2026PhaseNot applicableConditionsParkinson's diseaseParticipants12Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestSecondary13 weeks
  • Symbol CodingSecondary13 weeks
  • Choice Reaction TimeSecondary13 weeks
  • Simple Reaction TimeSecondary13 weeks
  • Finger Tapping TaskSecondary13 weeks
NCT07832981Start2026PhaseObservationalConditionsOther conditionsParticipants100Lead sponsorIndustryStatusNot yet recruitingLibrary tests named
  • Symbol CodingPrimary5 years
NCT07829029Start2022PhasePhase 4ConditionsOther conditionsParticipants270Lead sponsorOtherStatusRecruitingLibrary tests named
  • Trail Making TestSecondary6 months
  • Verbal LearningSecondary6 months
  • Digit Span TestSecondary6 months
  • Symbol CodingSecondary6 months

Page 1 of 59

Questions, answered from the data

How many clinical trials use Symbol Coding?

1,457 registered studies on ClinicalTrials.gov name it in an outcome measure, 451 of them in a primary outcome.

In which conditions do trials use Symbol Coding?

Most often in multiple sclerosis (375), depression and bipolar disorder (143) and dementia and Alzheimer's disease (117).

Do new trials use Symbol Coding more or less?

8.9% of the studies that started in 2021 to 2025 name it, against 8.9% of those that started in 2016 to 2020: about the same share.

Which tests do trials use with Symbol Coding?

The Trail Making Test (432 studies), Verbal Learning (416 studies) and the Digit Span Test (307 studies).

How many participants do phase 2 trials that use Symbol Coding enroll?

Half of the phase 2 studies that name it enroll 64 participants or fewer, and the middle half enroll 40 to 111. 183 of them give a size.

When do trials measure Symbol Coding?

Half of the primary outcomes that name Symbol Coding are measured within 12 weeks of the start, and the middle half from 3 weeks to 9 months. 420 primary outcomes give a duration.

How many completed trials that use Symbol Coding have reported results?

343 of the 695 completed studies that name it, 49%, have reported results: 190 posted them on ClinicalTrials.gov, 253 have a results paper linked to the registry record, and 100 did both. The other 352 show neither. Of all completed studies with a cognitive outcome, 46% have reported results.

More on tests in clinical trials

  • Symbol Key Game: what it measures, its scores, and a version to try
  • Symbol Coding: what it measures, its scores, and a version to try
  • All 101 tests in clinical trials
  • Cognitive tests by condition
  • Every registered study, by test, condition, phase and year

How the studies are counted

For each test family, the census runs ClinicalTrials.gov's own outcome search for the family's names and reads every study first posted by the day the family was counted. These studies were read on 10 November 2026. A study counts once on a page, however many tests it names. Counts for a test cover every version of the task under any of its names, so a page can count studies that used a commercial version.

The census adds two things to each record and changes nothing in it: which outcome list names the test (primary, then secondary, then other), and the condition groups, matched on the study's condition names and MeSH terms. A study can fall in several groups; one whose only condition is cognitive impairment or decline falls in “Cognitive impairment and decline”. Studies that name only instruments outside the library count in every total and share but are not listed.

A second read on 10 November 2026 added each study's overall status, whether results are posted, its intervention types, the countries of its sites and the time frame of the outcome that names each test. A time frame counts by the latest time point it names: “Baseline, 12 and 24 weeks” is 24 weeks, a single visit is within a day, and one that names no duration, such as “end of treatment”, is left out of the timings.

A third read on 10 November 2026 added the papers the registry links to each study: those its sponsor lists as reporting results, and those PubMed links to it through the study's NCT number. A study has a results paper when one of them came out in or after the month of its primary completion and PubMed does not class it as a protocol, review or comment. A paper that never gives the NCT number is not linked, so some studies counted as reporting neither did publish.

Source: ClinicalTrials.gov, a database of the U.S. National Library of Medicine, which does not endorse these pages. Every study line is in the data release 2.1.0, and the explorer's own file is clinical-trials-studies.json.

The census counts Symbol Key Game and Symbol Coding as one test family, so this page counts their studies together: 1,457 studies.

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